1. Field of the Invention
This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of a dual stage actuated suspension having shear-mode PZT actuators that rotate the gimbal tongue.
2. Description of Related Art
In a typical disk drive assembly, the suspension is the part that holds the read/write head over the correct position on a spinning data disk such as a magnetic data medium or optical data medium containing a number of concentric data tracks. The suspension typically includes a beam portion or load beam, and a flexure that includes a gimbaled portion, with the load beam typically mounted to a baseplate at the proximal end of the suspension, and the flexure mounted at the distal end of the load beam. The read/write head, or head slider, is affixed to the gimbaled portion of the flexure so that it can pitch and roll freely. The suspension is typically mounted at the end of an actuator arm, with the actuator arm moved by a voice coil motor (VCM).
Dual stage actuated (DSA) suspensions are well known. In a DSA suspension, the suspension is not only activated by the voice coil motor which moves the entire suspension, but an additional actuator is placed on the suspension itself for effecting fine movements of the head slider in order to keep it properly aligned over the correct data track on the spinning disk. The secondary actuator(s) provide finer control and higher bandwidth of the servo control loop than does the voice coil motor alone, which is only capable of effecting relatively coarse, slow movements of the suspension and hence the head slider. The secondary actuator(s) are sometimes referred to as milliactuators if they are mounted near the proximal end of the suspension, and microactuators if they are mounted near the distal end of the suspension. As used herein, the term “microactuator” will be used as an umbrella term that refers to any small actuator motor that is located on the suspension itself. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible.
In order to achieve the best performance in a suspension, it is important to maximize the stroke length in the microactuation mechanism. The term “stroke length” is a shorthand expression for the distance that the read/write head moves radially across a data disk per unit of voltage input to the microactuator motor.
Linear-mode PZTs are commonly used as microactuators on DSA suspension. U.S. Pat. No. 8,879,210 issued to Hahn et al. is an example of a DSA suspension that uses linear-mode PZTs to position the read/write head. The two PZTs act in push-pull fashion to rotate the head slider and thus to precisely position its read/write transducers.
D31 is the transverse piezoelectric coefficient of a linear-mode piezoelectric device; it represents the amount of linear expansion a PZT device undergoes in the transverse direction (i.e., normal to the electric field gradient) when an activation voltage is placed across the device's electrodes. D33 is the longitudinal piezoelectric coefficient; it represents the amount of linear expansion of a PZT in the longitudinal direction (i.e., in the direction of the electric field gradient) when an activation voltage is placed across the device's electrodes.